During the operation of flexographic printing presses, the flexographic printing plate on the plate cylinder tends to accumulate foreign matter, such as dried ink or ink build-up, paper, lint, clay, dirt and the like which must be removed in order to maintain quality printing. As a result, during an extended printing run, the flexographic plates must be either cleaned or replaced.
Flexographic printing plate cleaning has traditionally been a time-consuming, labor-intensive and expensive process. The presses must be completely stopped to permit manual access to the printing plates for plate cleaning. In the case of multiple color printing, i.e., wherein each color is printed by an individual printing unit, with the multiple, individual printing units closely aligned with each other, the individual printing units must be physically separated from each other to permit manual access to the flexographic printing plates mounted on the printing cylinders in order to clean the printing plates.
Typically, the flexographic printing plates are then cleaned by hand. In certain instances, the printing plates are cleaned while still mounted on the printing cylinder. In other instances, the printing plates are completely removed from the printing cylinder and cleaned separately. In either case, the cleaning process involves physically scrubbing the printing plates by hand with a mixture of water and detergent (in the situation wherein water-based inks are being used) or scrubbed with a solvent (in the situation wherein solvent-based inks are being used). In an extremely time-consuming process, during which time the presses remain stopped, this scrubbing is generally done with a brush, by hand. The scrubbed plates are then manually rinsed, often with a hose, to remove loosened foreign matter, along with excess detergent and ink residue. The free run-off of the rinsed material, however, is often uncontrolled and haphazard.
The rinsed plates are then hand-dried with a towel to remove excess moisture. However, such hand drying often leaves moisture in the crevices of the printing plates which negatively impact subsequent printing quality until the printing plates are completely dried through use.
The cleaned printing plates are then remounted on the printing cylinders, the multiple printing units are realigned, the printing presses are restarted and printing resumes. Problems with hand-cleaning of flexographic printing plates have resulted in incomplete or uneven scrubbing, incomplete or uneven drying, uncontrolled residue run-off, and excessive press down-time during the cleaning process.
In an alternative to the hand-cleaning of flexographic printing plates, the presses are stopped, multiple printing units are separated to be manually accessible and the dirty flexographic printing plates are removed from the press cylinders and replaced with new, clean plates. The dirty printing plates are then typically discarded. The process of replacing dirty, but unworn or undamaged printing plates is expensive and requires the repeated utilization of plate-manufacturing equipment and personnel.
In those instances wherein the printing job is extensive, dirty printing plates may need to be removed and either cleaned or replaced several times during the run of the job, thereby further increasing press down-time and added expense.